# 1041. Robot Bounded In Circle

On an infinite plane, a robot initially stands at `(0, 0)` and faces north. The robot can receive one of three instructions:

• `"G"`: go straight 1 unit;
• `"L"`: turn 90 degrees to the left;
• `"R"`: turn 90 degrees to the right.

The robot performs the `instructions` given in order, and repeats them forever.

Return `true` if and only if there exists a circle in the plane such that the robot never leaves the circle.

Example 1:

``````Input: instructions = "GGLLGG"
Output: true
Explanation: The robot moves from (0,0) to (0,2), turns 180 degrees, and then returns to (0,0).
When repeating these instructions, the robot remains in the circle of radius 2 centered at the origin.
``````

Example 2:

``````Input: instructions = "GG"
Output: false
Explanation: The robot moves north indefinitely.
``````

Example 3:

``````Input: instructions = "GL"
Output: true
Explanation: The robot moves from (0, 0) -> (0, 1) -> (-1, 1) -> (-1, 0) -> (0, 0) -> ...
``````

Constraints:

• `1 <= instructions.length <= 100`
• `instructions[i]` is `'G'``'L'` or, `'R'`.

``````class Solution {
public:
bool isRobotBounded(string instructions) {
int idx = 0; // 0 north, 1 east, 2 south, 3 west.
vector<int> cur{0, 0};
vector<vector<int>> dirs{{-1, 0}, {0, 1}, {1, 0}, {0, -1}};
for (char c : instructions) {
if (c == 'G') {
cur = {cur[0] + dirs[idx][0], cur[1] + dirs[idx][1]};
} else if (c == 'L') {
idx = (idx + 4 - 1) % 4;
} else {
idx = (idx + 1) % 4;
}
}
return (cur[0] == 0 && cur[1] == 0) || idx > 0;
}
};
``````

Github 同步地址:

https://github.com/grandyang/leetcode/issues/1041

https://leetcode.com/problems/robot-bounded-in-circle/

https://leetcode.com/problems/robot-bounded-in-circle/discuss/290856/JavaC%2B%2BPython-Let-Chopper-Help-Explain

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